Method and circuit arrangement for enhancing the contrast of an image

a technology of automatic enhancement and image contrast, applied in image enhancement, visual presentation, instruments, etc., can solve the problems of low image contrast, blurred images, dark and matt images, etc., and achieve the effect of enhancing the contrast of images

Inactive Publication Date: 2005-03-29
WI LAN INC
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

The present disclosure proposes an improved method and corresponding circuit arrangement for enhancing the contrast of an image comprising a plurality of pixels. In particular, the disclosed method and apparatus enables the contrast of the image to be enhanced, inter alia, as a function

Problems solved by technology

It is often the case with digitized images that the entire available dynamic range (i.e., the maximum possible resolution of the brightness values) is not utilized, which, however, results in a lower contrast of the image.
As a result, the images appear blurred, dark and matt when they are reproduced.
The previously referenced document, discussed above, does not make any s

Method used

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  • Method and circuit arrangement for enhancing the contrast of an image
  • Method and circuit arrangement for enhancing the contrast of an image
  • Method and circuit arrangement for enhancing the contrast of an image

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Embodiment Construction

According to the teachings of the present invention, the mean brightness is maintained (i.e., a pixel having a brightness corresponding to the mean brightness of the input image does not change its brightness upon application of the contrast enhancement). Additionally, straight-line functions having variable slope factors are used as the transformation functions, in which case the two straight-line functions intersect in particular at the mean brightness value xm and can be defined by the following functions:

ƒL(xk)=xm+(xk−xm)*aL|xk≦xm  (10)

ƒU(xk)=xm+(xk−xm)*aU|xk≧xm  (11)

In this case, xm denotes the mean brightness value, xk denotes the respective brightness value to be processed of the sub-image XL and XU, respectively, aL denotes the slope factor of the transformation function fL(xk) and aU denotes the slope factor of the transformation function fU(xk). The transformation function fL(xk) is exclusively applied to the pixels of the sub-image XL, which only has pixels having brightn...

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Abstract

A method and apparatus for enhancing the contrast of an image, where pixels of the image having a brightness less than a mean brightness of the image are transformed in accordance with a first straight-line function, and pixels having a brightness greater than the mean brightness of the image are transformed in accordance with a second straight-line function. Variable slope factors of the two straight-line functions are determined by an analysis of the brightness distribution of the transformed output image. The pixels, thus transformed, produce the contrast-enhanced output image.

Description

FIELD OF INVENTIONThe present invention relates to a method and a circuit arrangement for automatically enhancing the contrast of an image.BACKGROUND OF INVENTIONIt is often the case with digitized images that the entire available dynamic range (i.e., the maximum possible resolution of the brightness values) is not utilized, which, however, results in a lower contrast of the image. This applies, in particular, to older image originals (black / white feature films, etc), for example. As a result, the images appear blurred, dark and matt when they are reproduced.Known methods for enhancing contrast are based on the density distribution of the pixels in the image and spread the dynamic range of the image, with a result that the corresponding image is more brilliant and sharper. One example thereof is the so-called histogram spreading, which has the aim of producing the flattest possible density distribution in the image, which corresponds to a relatively large contrast. Mathematically, t...

Claims

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Application Information

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IPC IPC(8): H04N1/407G06T5/00H04N1/409
CPCH04N1/4074
Inventor SCHU, MARKUS
Owner WI LAN INC
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